1. Field of the Invention
The present invention relates to an image forming apparatus for forming a toner image on a continuous recording paper such as continuous forms by fixing a toner on the continuous recording paper.
2. Description of the Related Art
An image forming apparatus using an electrophotograpy, such as a copy machine, a laser printer, a facsimile machine, usually uses a printing method for forming a toner image by forming an unfixed toner image on a recording medium and fixing the toner image by applying heat and pressure to the unfixed toner image in a fixing apparatus.
A fixing apparatus usually uses a method of forming a fixed image by applying heat and pressure to a toner and a recording medium while the recording medium having an unfixed toner image is passed through a fixing part during conveyance of the recording medium having the unfixed toner image. The fixing part is formed between a rotating heating member of which surface is heated and a pressure member being pressed onto the heating member.
Such a recording medium used by the image forming apparatus, such as a paper, a cloth, an OHP sheet, etc., may be deformed due to expansion and contraction caused by changes in a temperature and humidity, heat and tension. Especially, such a deformation may occur in a roll paper which is wound on a core material and a continuous recording paper (continuous forms) folded at fixed intervals.
Such a deformation may be caused by a tension force applied to a recording paper while the recording paper is carried by conveyance rollers for a certain time when a printing operation is stopped. Moreover, a deformation may be generated in a continuous recording paper due to excessive heat being applied thereto when a portion of the recording paper was located in the vicinity of a fixing apparatus if the printing operation is interrupted due to a malfunction such as a paper jam. Such a deformation occurs in edge portions of the recording paper in many cases due to expansion and contraction of the recording paper in directions perpendicular to the conveyance direction of the recording paper caused by a heat and a tension force.
It is usual to improve a fixing performance in the fixing part by providing a pre-heating plate incorporating a heater inside thereof at a preceding stage of the fixing part to perform the fixing operation while previously applying heat to the toner and the recording paper. However, if the continuous recording paper is deformed partially, there may be a portion of the recording paper, which portion is not brought into contact with the pre-heating member. Such a partially deformed portion of the recording paper cannot be pre-heated sufficiently. Thus, a sufficient amount of heat cannot be provided to such a partially deformed portion of the recording paper even when the entire recording paper passes through the fixing part. Therefore, a fixing defect may be generated in the recording paper and it becomes difficult to acquire a satisfactory fixed image on the recording paper.
As measures for eliminating such a problem caused by generation of a deformation in a continuous recording paper, Japanese Patent Publication No. 3580882 discloses a recording pre-treatment method including a reformation step of reforming a deformation by conveying a portion of a recording paper including the deformation back and forth in a conveyance direction of the recording paper while applying a tension force to the recording paper by engaging the recording paper with conveyance rollers. This patent document also discloses a recording pre-treatment method including an ejecting step of ejecting a recording paper after cutting a portion of the recording paper, which portion includes a deformation, by a cutting mechanism for the recording paper.
According to the recording pre-treatment methods disclosed in the above-mentioned Japanese Patent Publication No. 3580882, a deformed portion of the recording paper is automatically reformed or the deformed portion is automatically ejected to outside the apparatus. Thus, a defective printing such a drop of an image and a printing failure such as a paper jamming may be prevented beforehand because the recording paper used for printing is set in a normal state.
However, there is a case where the pre-treatment methods disclosed in the above-mentioned patent document cannot completely reform or correct a deformed portion of a continuous recording paper (continuous forms). Additionally, there may be a case where it is difficult to cut out and eject a deformed portion of a recording paper by recognizing an accurate position of the deformed portion of the recording paper where a deformation is generated. Further, a manufacturing cost of a printing apparatus may be increased because an additional mechanism, such as a forward and rearward conveyance mechanism of a recording paper and a paper cutting mechanism, must be incorporated into the printing apparatus.